Astronomers have identified what they think is the largest galaxy ever observed, more than 60 times the size of the Milky Way. They believe that in its tremendous mass they may find clues to forces responsible for the clustering of matter in the universe. The galaxy, embracing more than 100-trillion stars, is the extremely bright object at the center of a rich cluster of galaxies known as Abell 2029.
Analysis of new telescopic images indicates that the object is a distinct galaxy more than 6-million light years in diameter, scientists report in the issue of the journal Science published today.
Until now the largest known galaxy was Markarian 348, which is about 1.3-million light years wide. The Milky Way, Earth's home galaxy, is about 100,000 light years across. A light year, the distance a beam of light moving at 186,000 miles a second will travel in a year, is roughly 6-trillion miles.
The dense core of the Abell cluster of galaxies had been studied before, but the new images from the Kitt Peak National Observatory in Arizona enabled astronomers to see its faint fringes for the first time and measure the galaxy's true extent.
The core galaxy, one of the most luminous ever seen, emits more than one quarter of the total light from the galaxy cluster.
"This is an organized mass of light and energy," said Dr. Jeffrey R. Kuhn, an astronomer at Michigan State University and one of the discoverers. "Since it's a smooth distribution, the outer part really is connected to the inner part. It's a very large, organized galaxy."
Dr. Juan M. Uson of the National Radio Astronomy Observatory in Socorro, N.M., is the leader of the research team which also included Dr. Stephen P. Boughn of Haverford College in Pennsylvania.
The astronomers said the density, luminosity and smoothness of the large galaxy were possible clues to its formation and to the nature of invisible matter _ dark matter or the missing mass _ that makes up most of the universe.
If prevailing cosmological theory is correct, nearly 99 percent of the universe is unobservable because the matter emits no radiation at all. It is this missing mass that presumably provides the gravitational force accounting for large-scale structure, such as galaxies, clusters of galaxies and superclusters.
"This is just the beginning of a program to look for faint light in clusters that may give us some idea of where the missing mass is," Kuhn said.
The astronomers also said that the even distribution of stars and other matter in the galaxy suggested that it must be an extremely old structure. It was probably created at the same time as the rest of the cluster and may have been the keystone in the cluster's formation.
Other astrophysicists acknowledged that the formation of galaxies and other large structures is one of the major problems in cosmology and that the new findings, if confirmed by more observations, could resolve some of the issues.